Graphical computer objects, particularly 1D, 2D or 3D graphics (graphical) objects, are most commonly stored in memory or in a file as a set of triangles with 3 coordinates (x, y, and z) representing the vertices of each triangle. The rendering and display of 1D, 2D or 3D graphics models results from the transformation and rendering of these triangles from a 1D, 2D (or 3D) object space to a 2D image space represented by the displays framebuffer. In the simplest case, these models are transformed and rendered as wireframe (lines) objects with a single color representing the wireframe lines. A more common approach is to render these models as filled polygons (triangles). The process of filling a triangle is called scan conversion and can be performed in various ways to achieve different visual effects. Generally, the different forms of filling a triangle fall into one of 3 categories. In the simplest case, each interior pixel (picture element) of the triangle in image space is identified and assigned the same color (R,G,B) value. The value is stored in the display framebuffer at the computed location. This is type of filling is called flat shading since there is no variation in the colors stored across the interior of the triangle. In other words there is 1 color per triangle. In another case, a pre-existing picture or pattern may be mapped across the interior of the triangle. This technique is known as texture mapping. A third case is smooth shading, where the color of the triangle interior varies from pixel to pixel. Smooth shading is usually performed by the algorithms such as Gouraud or Phong shading. In Gouraud shading a color is assigned to each vertex or the triangle and used to compute the rate of change of each color component (R, G, B) over the interior of the triangle. Phong shading differs slightly in that normal vectors are assigned to each vertex and are interpolated across the interior pixels of the triangle. A normal vector is a vertex attribute which relates to how light will be reflected when it strikes that vertex or the polygon that the vertex is part of. At each pixel location a new normal is computed and used in a lighting equation to compute a color at that pixel location. This is generally considered a more accurate form of shading a triangle although computationally much more expensive. In every form of smooth shading, there exists the probability of generating new colors, i.e. R,G,B values not represented by the original values attached to each vertex of the polygon. With limited display memory this becomes problematic. A more detailed explanation of computer graphics can be found in textbooks such as Computer Graphics: Principles and Practice by Fole,van Dam, Feiner, & Hughes, pp. 598–599,613,736–740 or Real-time Rendering by Moller and Haines, pp 14,68–69, 77, which are herein incorporated by reference in their entirety.